System for enhanced gas turbine performance in a liquefied natural gas facility

ABSTRACT

A system for liquefying natural gas that includes a process and apparatus for enhancing the performance of one or more gas turbines. Gas turbine power output can be stabilized or even enhanced using the interstage cooling system configured according to one or more embodiments of the present invention. In one embodiment, partially compressed air from a lower compression stage of a gas turbine is cooled via indirect heat exchange with a primary coolant before being returned to a higher compression stage of the same gas turbine. Optionally, the interstage cooling system can employ one or more secondary coolants to remove the rejected heat from the primary coolant system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority benefit under 35 U.S.C. Section 119(e)of U.S. Provisional Patent Ser. No. 61/095,469 filed on Sep. 9, 2008,the entire disclosure of which is incorporated herein by reference.

BACKGROUND

1. Field of the Invention

This invention relates to methods and apparatuses for liquefying naturalgas. In another aspect, the invention concerns a liquefied natural gas(LNG) facility employing a cooling system operable to enhance theperformance of one or more gas turbines used in the LNG facility.

2. Description of Related Art

Cryogenic liquefaction is commonly used to convert natural gas into amore convenient form for transportation and/or storage. Becauseliquefying natural gas greatly reduces its specific volume, largequantities of natural gas can be economically transported and/or storedin liquefied form.

Transporting natural gas in its liquefied form can effectively link anatural gas source with a distant market when the source and market arenot connected by a pipeline. This situation commonly arises when thesource of natural gas and the market for the natural gas are separatedby large bodies of water. In such cases, liquefied natural gas (LNG) canbe transported from the source to the market using specially designedocean-going LNG tankers.

Storing natural gas in its liquefied form can help balance periodicfluctuations in natural gas supply and demand. In particular, LNG can be“stockpiled” for use when natural gas demand is low and/or supply ishigh. As a result, future demand peaks can be met with LNG from storage,which can be vaporized as demand requires.

Several methods exist for liquefying natural gas. Some methods produce apressurized LNG (PLNG) product that is useful, but requires expensivepressure-containing vessels for storage and transportation. Othermethods produce an LNG product having a pressure at or near atmosphericpressure. In general, these non-pressurized LNG production methodsinvolve cooling a natural gas stream via indirect heat exchange with oneor more refrigerants and then expanding the cooled natural gas stream tonear atmospheric pressure. In addition, most LNG facilities employ oneor more systems to remove contaminants (e.g., water, acid gases,nitrogen, and ethane and heavier components) from the natural gas streamat different points during the liquefaction process.

Typically, LNG facilities employ one or larger, multi-stage refrigerantcompressors to circulate refrigerant used to cool the natural gas feedstream processed in the facility. These industrial compressors are oftendriven by gas turbines, which combust fuel with a stream of compressedair to generate power that can then be utilized to drive the compressor.The performance of these gas turbines, which can generally be correlatedto the turbine's power output and efficiency, is highly dependent onambient air conditions. For example, increases in ambient airtemperature typically lead to decline in turbine power output.Reductions in turbine power output translate to diminished compressorperformance, which, ultimately translates to reduced LNG production.Thus, it may be desirable to maintain and/or increase LNG productionthrough enhanced gas turbine operation.

SUMMARY

In one embodiment of the present invention, there is provided a processfor liquefying a natural gas stream, said process comprising: (a)cooling at least a portion of said natural gas stream via indirect heatexchange with a first refrigerant in a first refrigeration cycle tothereby produce a cooled natural gas stream; (b) further cooling atleast a portion of said cooled natural gas stream via indirect heatexchange with a second refrigerant in a second refrigeration cycle tothereby provide a further cooled natural gas stream; and (c) cooling apartially compressed air stream via indirect heat exchange with aprimary coolant to thereby provide a cooled partially compressed airstream, wherein said partially compressed air stream is withdrawn froman intermediate compression stage of a gas turbine used to drive atleast one refrigerant compressor associated with said first and/or saidsecond refrigeration cycle.

In another embodiment of the present invention, there is provided aprocess for liquefying a natural gas stream, said process comprising:(a) compressing a first refrigerant stream in a first refrigerantcompressor to thereby provide a first compressed refrigerant stream,wherein said first refrigerant compressor is at least partially drivenby a first gas turbine; (b) cooling a first air stream via indirect heatexchange with at least a portion of said first refrigerant in a firstheat exchanger to thereby provide a first cooled air stream; and (c)introducing at least a portion of said first cooled air stream into saidfirst gas turbine.

In yet another embodiment of the present invention there is provided aliquefied natural gas (LNG) facility comprising a first refrigerationcycle and a first heat exchange zone. The first refrigeration cyclecomprises a first refrigerant compressor, a first refrigerant chiller,and a first gas turbine. The first refrigerant compressor is operable toproduce a compressed first refrigerant stream and first refrigerantchiller is operable to cool a natural gas stream via indirect heatexchange with the compressed first refrigerant stream. The firstcompressor is driven by the first gas turbine, which is a multi-stage,multi-shaft gas turbine comprising a first low compression stage and afirst high compression stage. The first heat exchange zone is operableto cool a first partially compressed air stream withdrawn from the firstlow compression stage via indirect heat exchange with a first coolant tothereby produce a first cooled air stream. The first high compressionstage is configured to receive the first cooled air stream.

BRIEF DESCRIPTION OF THE FIGURES

Certain embodiments of the present invention are described in detailbelow with reference to the enclosed figures, wherein:

FIG. 1 is a simplified overview of compressor/driver system including aninterstage cooling zone configured according to one embodiment of thepresent invention;

FIG. 2 is a simplified overview of a compressor/driver system includingan interstage cooling zone configured according to another embodiment ofthe present invention;

FIG. 3 is a simplified overview of a cascade-type LNG facilityconfigured in accordance with one embodiment of the present invention;

FIG. 4a is a schematic diagram of an LNG facility configured inaccordance with one embodiment of the present invention with portions ofthe LNG facility connected to lines A, B, C, D, E, F, G, H, and I beingillustrated in FIG. 4 b;

FIG. 4b . is a schematic diagram of an interstage cooling systemconfigured according to one embodiment of the present invention that isintegrated into the portion of the LNG facility illustrated in FIG. 4avia lines A, B, C, D, E, F, G, H, and I;

FIG. 5a is a schematic diagram of an LNG facility configured inaccordance with another embodiment of the present invention withportions of the LNG facility connected to lines A, B, C, D, E, F, G, H,I, J, K, and L being illustrated in FIG. 5b ; and

FIG. 5b . is a schematic diagram of an interstage cooling systemconfigured according to another embodiment of the present invention thatis integrated into the portion of the LNG facility illustrated in FIG.5a via lines A, B, C, D, E, F, G, H, I, J, K, and L.

DETAILED DESCRIPTION

Referring first to FIG. 1, a schematic diagram of compressor-driversystem 410 employing an interstage cooling system is generallyillustrated as comprising a gas turbine 412 mechanically coupled to andoperable to power a compressor 414. In one embodiment, gas turbine 412can be directly coupled to compressor 414, while, in another embodiment,gas turbine 412 can be indirectly coupled to compressor 414 via a speedmanipulating device 431, as shown in FIG. 1. Examples of speedmanipulating devices can include, but are not limited to, gear boxes ortorque converters. In addition, compressor/driver system 410 comprisesan interstage air cooler 440, operable to cool at least a portion of thepartially compressed air stream exiting one or more compression stagesof gas turbine 412.

Gas turbine 412 can be any commercially available industrial gasturbine. Gas turbine 412 can comprise a single shaft or a multi-shaftconfiguration and can comprise a frame gas turbine, a modular gasturbine, an aeroderivative gas turbine, or any combination thereof.Examples of suitable frame gas turbines can include, but are not limitedto a single-shaft GE Frame-5, Frame-6, Frame-7, or Frame-9 gas turbinesavailable from GE Power Systems, Atlanta, Ga. or the equivalent thereof.Examples of modular gas turbines can include Siemens SGT-600 or SGT-700gas turbines (available from Siemens AG in Erlangen, Germany) and SolarMars® or Titan™ gas turbines (available from Solar Turbines Incorporatedin Peoria, Ill.) or the equivalent thereof. Examples of aeroderivativegas turbines can include, but are not limited to, a GE LM1600, LM2000,LM2500, LM2500+, LM6000, or LMS-100® (available from GE Power Systems inAtlanta, Ga.) or the equivalent thereof.

In one embodiment illustrated in FIG. 1, gas turbine 412 can have athree-shaft configuration. According to this embodiment, gas turbine 412can comprise a low pressure compression stage 416, a high pressurecompression stage 418, a combustion chamber 420, a high pressure turbine422, a low pressure turbine 424, and an optional power turbine 426. Inone embodiment illustrated in FIG. 1, power turbine 426 can be directlyor indirectly mechanically coupled to low pressure compression stage 416and compressor 414 via a first inner concentric shaft 430. In anotherembodiment, gas turbine 412 may not include power turbine 426. Lowpressure compression stage 416 and low pressure expansion stage 424 canbe mechanically coupled via a second concentric inner shaft 432, whilehigh pressure compression stage 418 and high pressure expansion stage426 are drivingly coupled by a third concentric outer shaft 434, asillustrated in FIG. 1.

Compressor 414 can be any type of multi-stage industrial compressorcapable of sequentially compressing a gaseous stream to successivelyhigher pressures. In one embodiment compressor 414 can have at leastone, at least 2, or at least 3 compression stages (not shown).Multistage compressor 414 can be a centrifugal compressor, an axialcompressor, or any combination thereof.

In general, interstage cooler 440 can be any heat exchanger operable tocool the incoming stream of partially compressed air withdrawn from lowpressure compression stage 416 by at least about 1° C. (1.8° F.), atleast about 2° C. (3.6° F.), at least about 5° C. (9° F.), or at least8° C. (14.4° F.). In another embodiment, interstage cooler 440 can coolthe partially compressed air stream in conduit 452 by no more than 25°C. (45° F.), no more than 20° C. (36° F.), no more than 15° C. (27° F.),or no more than 10° C. (18° F.). In one embodiment, interstage cooler440 can comprise a direct heat exchanger that employs one or more directheat exchange methods. Examples of suitable direct heat exchange methodsinclude, inlet fogging, misting, and wet compression techniques. Wheninterstage cooler 440 employs a direct heat exchanger, one or moresuitable heat transfer fluids, such as, for example, water, alcohols, orlight hydrocarbons, may be employed. In another embodiment, interstagecooler 440 can comprise an indirect heat exchanger. Examples of suitableindirect heat exchangers can include, but are not limited to, ashell-and-tube heat exchanger, a core-in-kettle heat exchanger, and aplate-fin heat exchanger. When interstage cooler 440 employs an indirectheat exchanger, one or more suitable heat transfer fluids, including,for example, water, glycols, alcohols, commercially available heattransfer fluids, and any combination thereof can be employed ininterstage cooler 440.

Turning now to the operation of compressor/driver system 410 illustratedin FIG. 1, an uncompressed stream of inlet air in conduit 450 can beintroduced into an inlet of low pressure compression stage 416 of gasturbine 412. The combustion air stream can then be at least partiallycompressed and at least a portion of the resulting stream can bewithdrawn from low pressure compression stage 416 via conduit 452. Ifpresent, the remaining partially compressed air stream can pass to highcompression stage 418, as illustrated by the dashed line in FIG. 1.

Thereafter, the at least partially compressed stream in conduit 452 canbe introduced into an interstage air cooler 440, wherein at least aportion of the stream can be cooled via an indirect heat exchange with acoolant in conduit 442, as shown in FIG. 1. The coolant can comprise anysuitable heat transfer fluid capable of removing at least a portion ofthe heat from the partially compressed air stream in conduit 452. Thecoolant can comprise water, glycols, alcohols, light hydrocarbons, andany combination thereof. Specific configurations employing differenttypes of refrigerants will be discussed in detail shortly, with respectto FIGS. 3, 4 a, 4 b, 5 a, and 5 b. As shown in FIG. 1, the resulting,cooled, partially compressed air stream in conduit 454 can then beintroduced into high pressure compression stage 418, as shown in FIG. 1.

As illustrated in FIG. 1, the compressed air stream exiting highpressure compression stage 418 via conduit 458 can subsequently beintroduced into combustion chamber 420, wherein the air stream can becombusted with a fuel gas introduced into combustion chamber 420 viaconduit 460. The warm combustion gases exiting combustion chamber 420can be sequentially expanded in high stage expansion stage 422, lowstage expansion stage 424, and power turbine 426. The resulting energy,which can be at least partially translated into rotational energy, canbe used to respectively power low pressure compression stage 416 (viafirst inner concentric shaft 432), high compression stage 422 (via outerconcentric shaft 434), and load (e.g., driven) compressor 414 (viasecond inner concentric shaft 430).

In general, cooling an at least partially compressed air streamwithdrawn from the low pressure compression stage prior to reintroducingthe cooled stream into the high pressure compression stage can increasethe power output of the gas turbine by at least about 10 percent, atleast about 15 percent, at least about 20 percent, or at least 25percent, as compared to the power output of a gas turbine that does notemploy this type of interstage cooling. In one embodiment, interstageair cooler 440 can be operable to cool the stream of partiallycompressed air in conduit 452 by an amount in the range of from about 1to about 25° C., about 2 to about 20° C., or 5 to 15° C. Typically, theair stream in conduit 452 can have a temperature greater than about 20°C. (68° F.), greater than about 25° C. (77° F.), or greater than 30° C.(86° F.), while the stream in conduit 454 can have a temperature lessthan about 15° C. (59° F.), less than about 10° C. (50° F.), or lessthan 5° C. (41° F.).

Another embodiment of a simplified compressor/driver system 510employing an interstage cooler 540 is illustrated in FIG. 2. Theconfiguration and operation of the compressor/driver system 510illustrated in FIG. 2 is similar to that as previously described in FIG.1, except interstage cooler 540 of compressor/driver system 510 furtherincludes a means for additionally cooling the inlet combustion airstream introduced into low pressure compression stage 516 of gas turbine512. The operation of compressor/driver system 510 illustrated in FIG.2, as it differs from the operation of compressor/driver system 410previously described with respect to FIG. 1, will now be discussed indetail.

A stream of uncompressed inlet air in conduit 550 enters interstagecooler 540, wherein the stream can be cooled via indirect heat exchangewith a coolant stream entering interstage cooler 540 via conduit 542. Inone embodiment, interstage cooler 540 can be operable to cool theincoming uncompressed air stream by at least about 2° C. (3.6° F.), atleast about 5° C. (9° F.), at least about 8° C. (14.4° F.), or at least10° C. (18° F.). Generally, the temperature of the air stream in conduit550 can be greater than about 8° C. (46° F.), at least about 10° C. (50°F.), at least about 15° C. (59° F.), about 25° C. (77° F.), greater thanabout 30° C. (86° F.), greater than about 32° C. (90° F.), greater thanabout 35° C. (95° F.), or greater than about 37° C. (98° F.), while thetemperature of the cooled air stream withdrawn from interstage cooler540 via conduit 551 can be less than about 20° C. (68° F.), less thanabout 15° C. (59° F.), less than about 10° C. (50° F.), or less than 5°C. (41° F.). Although illustrated as a single heat exchanger in FIG. 2,in another embodiment, interstage cooler 540 can comprise two or moreseparate heat exchangers, each capable of cooling at least a portion ofthe combustion air and/or partially compressed air streams associatedwith gas turbine 512.

As shown in FIG. 2, the cooled air stream in conduit 551 can then beintroduced into the combustion air inlet of low pressure compressionstage 516 of gas turbine 512. Subsequently, a stream of partiallycompressed air withdrawn from the outlet of low pressure compressionstage 516 can be routed to interstage cooler 540 can continue throughcompressor/driver system 510 in an analogous manner as discussed indetail previously with respect to FIG. 1.

According to one embodiment, the present invention can be implemented ina facility used to cool natural gas to its liquefaction temperature tothereby produce liquefied natural gas (LNG). The LNG facility generallyemploys one or more refrigerants to extract heat from the natural gasand then reject the heat to the environment. Numerous configurations ofLNG systems exist, and the present invention may be implemented in manydifferent types of LNG systems.

In one embodiment, the present invention can be implemented in a mixedrefrigerant LNG system. Examples of mixed refrigerant processes caninclude, but are not limited to, a single refrigeration system using amixed refrigerant, a propane pre-cooled mixed refrigerant system, and adual mixed refrigerant system. In general, mixed refrigerants cancomprise hydrocarbon and/or non-hydrocarbon components. Examples ofsuitable hydrocarbon components typically employed in mixed refrigerantscan include, but are not limited to, methane, ethane, ethylene, propane,propylene, as well as butane and butylene isomers. Non-hydrocarboncomponents generally employed in mixed refrigerants can include carbondioxide and nitrogen. Mixed refrigerant processes employ at least onemixed component refrigerant, but can additionally employ one or morepure-component refrigerants as well.

In another embodiment, the present invention is implemented in a cascadeLNG system employing a cascade-type refrigeration process using one ormore pure component refrigerants. The refrigerants utilized incascade-type refrigeration processes can have successively lower boilingpoints in order to maximize heat removal from the natural gas streambeing liquefied. Additionally, cascade-type refrigeration processes caninclude some level of heat integration. For example, a cascade-typerefrigeration process can cool one or more refrigerants having a highervolatility via indirect heat exchange with one or more refrigerantshaving a lower volatility. In addition to cooling the natural gas streamvia indirect heat exchange with one or more refrigerants, cascade andmixed-refrigerant LNG systems can employ one or more expansion coolingstages to simultaneously cool the LNG while reducing its pressure tonear atmospheric pressure.

FIG. 3 illustrates one embodiment of a simplified LNG facility employinga turbine inlet air cooling system capable of increasing the efficiencyand power of one or more gas turbines employed therein. The cascade-typeLNG facility of FIG. 3 generally comprises a cascade cooling section 10,a heavies removal zone 11, and an expansion cooling section 12. Cascadecooling section 10 is depicted as comprising a first mechanicalrefrigeration cycle 13, a second mechanical refrigeration cycle 14, anda third mechanical refrigeration cycle 15. In general, first, second,and third refrigeration cycles 13, 14, 15 can be closed-looprefrigeration cycles, open-loop refrigeration cycles, or any combinationthereof. In one embodiment of the present invention, first and secondrefrigeration cycles 13 and 14 can be closed-loop cycles, and thirdrefrigeration cycle 15 can be an open-loop cycle that utilizes arefrigerant comprising at least a portion of the natural gas feed streamundergoing liquefaction.

In accordance with one embodiment of the present invention, first,second, and third refrigeration cycles 13, 14, 15 can employ respectivefirst, second, and third refrigerants having successively lower boilingpoints. For example, the first, second, and third refrigerants can havemid-range boiling points at standard pressure (i.e., mid-range standardboiling points) within about 10° C. (18° F.), within about 5° C. (9°F.), or within 2° C. (3.6° F.) of the standard boiling points ofpropane, ethylene, and methane, respectively. In one embodiment, thefirst refrigerant can comprise at least about 75 mole percent, at leastabout 90 mole percent, at least 95 mole percent, or can consistessentially of propane, propylene, or mixtures thereof. The secondrefrigerant can comprise at least about 75 mole percent, at least about90 mole percent, at least 95 mole percent, or can consist essentially ofethane, ethylene, or mixtures thereof. The third refrigerant cancomprise at least about 75 mole percent, at least about 90 mole percent,at least 95 mole percent, or can consist essentially of methane.

As shown in FIG. 3, each of first, second, and third refrigerationcycles 13, 14, 15 employ respective first, second, and third refrigerantcompressors 16, 19, 22, to compress the first, second, and thirdrefrigerants used to cool the natural gas feed stream. In general, eachof first, second, and third refrigerant compressors 16, 19, 22 compriselarge, multi-stage compressors driven by one or more gas turbines 16 a,19 a, and 22 a. Although illustrated in FIG. 3 as single gas turbines,in one embodiment, compressor 16, 19, and/or 22 can be driven by two ormore turbines. In another embodiment, first, second, and thirdrefrigerant compressors 16, 19, 22 can each comprise two or morecompressors driven by at least one gas turbine 16 a, 19 a, 22 a.Typically, this configuration can be useful when LNG facility 10comprises at least one production train. In general, each gas turbine 16a, 19 a, 22 a can combust a fuel gas stream with a stream of filteredambient air to thereby provide energy to drive an expander. This energyis then at least partially translated into rotational energy, which canbe used to drive refrigerant compressors 16, 19, 22 via a common shaft.

Gas turbines 16 a, 19 a, 22 a, can be any commercially availableindustrial gas turbine. In general, gas turbines 16 a, 19 a, and/or 22 acan have a single shaft or a multi-shaft configuration. Typically,multi-shaft gas turbines can comprise two (i.e., dual-shaft) or three(i.e., triple-shaft) shafts, but other multi-shaft turbines are equallysuitable. The plurality of shafts employed in a multi-shaft gas turbinecan be concentric or can be positioned substantially parallel to oneanother. Single shaft gas turbines can also comprise an auxiliary or“helper” motor to provide supplemental power during turbine start up.Additional details regarding specific types of gas turbines werediscussed previously with respect to FIG. 1.

As shown in FIG. 3, LNG facility 10 can further comprise a plurality ofinterstage coolers 25 a-c operable to cool one or more partiallycompressed streams originating from gas turbines 16 a, 19 a, and 22 avia direct and/or indirect heat exchange with a primary coolant inconduits P1, P2, and P3. As illustrated in FIG. 3, primary coolantintroduced into and withdrawn from interstage coolers 25 a-c canoriginate from coolant sources 26 a-c. In general, coolant sources 26a-c can be any suitable mechanical, thermal, or absorptive heat sinkscapable of removing at least a portion of heat stored in the warmedprimary coolant streams withdrawn from interstage coolers 25 a-c.According to one embodiment, coolant sources 26 a-c can comprisemultiple zones within a single coolant system; while, according toanother embodiment, coolant sources 26 a-c can comprise one or moreindependent coolant systems. In one embodiment illustrated in FIG. 3,coolant sources 26 a-c can employ streams of secondary coolant inconduits S1, S2, S3 to remove at least a portion of the heat stored inwarmed primary coolant streams in conduits P1, P2, P3 via direct and/orindirect heat exchange. As shown in FIG. 3, the resulting cooled primarycoolant streams can be re-employed in interstage coolers 25 a-c and cancontinue as previously discussed.

Primary and secondary coolant streams can comprise any suitable heattransfer fluid and combinations thereof. Primary and/or secondarycoolant streams can comprise hydrocarbon refrigerants, non-hydrocarbonrefrigerants, and combinations thereof. According to one embodiment, theprimary and/or secondary coolants can comprise water, glycols, and/oralcohols or can be one or more commercially available heat transfermedia, such as, for example, DOWFROST™ (commercially available from DowChemical Company, Midland, Mich.). In another embodiment, the primaryand/or secondary coolant can comprise air, nitrogen, or carbon dioxide.In yet another embodiment, primary and/or secondary coolant streams cancomprise a portion of one or more of the first, second, and/or thirdrefrigerants employed in first, second, and/or third refrigerationcycles 13, 14, 15 of LNG facility 10, depicted in FIG. 3. Specificconfigurations of interstage coolers 25 a-c and coolant sources 26 a-cwill be discussed in detail shortly with respect to FIGS. 4a, 4b, 5a ,and 5 b.

Turning back to FIG. 3, in addition to first refrigerant compressor 16,first refrigeration cycle 13 can comprise a first cooler 17 and a firstrefrigerant chiller 18. First refrigerant compressor 16 can discharge astream of compressed first refrigerant, which can subsequently be cooledand at least partially liquefied in cooler 17. The resulting refrigerantstream can then enter first refrigerant chiller 18, wherein at least aportion of the refrigerant stream can cool the incoming natural gasstream in conduit 100 via indirect heat exchange with the vaporizingfirst refrigerant. The gaseous refrigerant can exit first refrigerantchiller 18 and can then be routed to an inlet port of first refrigerantcompressor 16 to be recirculated as previously described.

First refrigerant chiller 18 can comprise one or more cooling stagesoperable to reduce the temperature of the incoming natural gas stream inconduit 100 by an amount in the range of from about 20° C. (36° F.) toabout 120° C. (216° F.), about 25° C. (45° F.) to about 110° C. (198°F.), or 40° C. (72° F.) to 85° C. (153° F.). Typically, the natural gasentering first refrigerant chiller 18 via conduit 100 can have atemperature in the range of from about −20° C. (−4° F.) to about 95° C.(203° F.), about −10° C. (14° F.) to about 75° C. (167° F.), or 10° C.(50° F.) to 50° C. (122° F.). In general, the temperature of the coolednatural gas stream exiting first refrigerant chiller 18 can be in therange of from about −55° C. (−67° F.) to about −15° C. (5° F.), about−45° C. (−49° F.) to about −20° C. (−4° F.), or −40° C. (−40° F.) to−30° C. (−22° F.). In general, the pressure of the natural gas stream inconduit 100 can be in the range of from about 690 kPa (100.1 psi) toabout 20,690 kPa (3,000.8 psi), about 1,725 kPa (250.2 psi) to about6,900 kPa (1,000.8 psi), or 2,760 kPa (400.3 psi) to 5,500 kPa (797.7psi). Because the pressure drop across first refrigerant chiller 18 canbe less than about 690 kPa (100.1 psi), less than about 345 kPa (50psi), or less than 175 kPa (25.4 psi), the cooled natural gas stream inconduit 101 can have substantially the same pressure as the natural gasstream in conduit 100.

As illustrated in FIG. 3, the cooled natural gas stream (also referredto herein as the “cooled predominantly methane stream”) exiting firstrefrigeration cycle 13 can then enter second refrigeration cycle 14,which can comprise a second refrigerant compressor 19, a second cooler20, and a second refrigerant chiller 21. Compressed refrigerant can bedischarged from second refrigerant compressor 19 and can subsequently becooled and at least partially liquefied in cooler 20 prior to enteringsecond refrigerant chiller 21. Second refrigerant chiller 21 can employa plurality of cooling stages to progressively reduce the temperature ofthe predominantly methane stream in conduit 101 by an amount in therange of from about 30° C. (54° F.) to about 100° C. (180° F.), about35° C. (63° F.) to about 85° C. (153° F.), or 50° C. (90° F.) to 70° C.(126° F.) via indirect heat exchange with the vaporizing secondrefrigerant. As shown in FIG. 3, the vaporized second refrigerant canthen be returned to an inlet port of second refrigerant compressor 19prior to being recirculated in second refrigeration cycle 14, aspreviously described.

The natural gas feed stream in conduit 100 will usually contain ethaneand heavier components (C₂+), which can result in the formation of a C₂+rich liquid phase in one or more of the cooling stages of secondrefrigeration cycle 14. In order to remove the undesired heaviesmaterial from the predominantly methane stream prior to completeliquefaction, at least a portion of the natural gas stream passingthrough second refrigerant chiller 21 can be withdrawn via conduit 102and processed in heavies removal zone 11, as shown in FIG. 3. The streamin conduit 102 can have a temperature in the range of from about −110°C. (−166° F.) to about −45° C. (−49° F.), about −95° C. (−139° F.) toabout −50° C. (−58° F.), or −85° C. (−121° F.) to −65° C. (−85° F.).Typically, the stream in conduit 102 can have pressure that is withinabout 5 percent, about 10 percent, or 15 percent of the pressure of thenatural gas feed stream in conduit 100.

Heavies removal zone 11 can comprise one or more gas-liquid separatorsoperable to remove at least a portion of the heavy hydrocarbon materialfrom the predominantly methane stream. Typically, heavies removal zone11 can be operated to remove benzene and other high molecular weightaromatic components, which can freeze in subsequent liquefaction stepsand plug downstream process equipment. In addition, heavies removal zone11 can be operated to recover the heavy hydrocarbons in a natural gasliquids (NGL) product stream. Examples of typical hydrocarbon componentsincluded in NGL streams can include ethane, propane, butane isomers,pentane isomers, and hexane and heavier components (i.e., C₆+). Theextent of NGL recovery from the predominantly methane stream ultimatelyimpacts one or more final characteristics of the LNG product, such as,for example, Wobbe index, BTU content, higher heating value (HHV),ethane content, and the like. In one embodiment, the NGL product streamexiting heavies removal zone 11 can be subjected to furtherfractionation in order to obtain one or more pure component streams.Often, NGL product streams and/or their constituents can be used asgasoline blendstock.

As shown in FIG. 3, a heavies-depleted, predominantly methane stream canbe withdrawn from heavies removal column 25 via conduit 103 and can berouted back to second refrigeration cycle 14. Generally, the stream inconduit 103 can have a temperature in the range of from about −100° C.(−148° F.) to about −40° C. (−40° F.), about −90° C. (−130° F.) to about−50° C. (−58° F.), or −80° C. (−112° F.) to −55° C. (−67° F.). Thepressure of the stream in conduit 103 can typically be in the range offrom about 1,380 kPa (200.15 psi) to about 8,275 kPa (1200.2 psi), about2,420 kPa (351 psi) to about 5,860 kPa (849.9 psi), or 3,450 kPa (500.4psi) to 4,830 kPa (700.5 psi).

As shown in FIG. 3, the predominantly methane stream in conduit 103 cansubsequently be further cooled via second refrigerant chiller 21. In oneembodiment, the stream exiting second refrigerant chiller 21 via conduit104 can be completely liquefied and can have a temperature in the rangeof from about −135° C. (−211° F.) to about −55° C. (−67° F.), about−115° C. (−175° F.) to about −65° C. (−85° F.), or −95° C. (−139° F.) to−85° C. (−121° F.). Generally, the stream in conduit 104 can be atapproximately the same pressure the natural gas stream entering the LNGfacility in conduit 100.

As illustrated in FIG. 3, the pressurized LNG-bearing stream in conduit104 can combine with a stream in conduit 109 prior to entering thirdrefrigeration cycle 15, which is depicted as generally comprising athird refrigerant compressor 22, a cooler 23, and a third refrigeranteconomizer 24. Compressed refrigerant discharged from third refrigerantcompressor 22 enters cooler 23, wherein the refrigerant stream is cooledvia indirect heat exchange prior to entering cooling zone 29. Coolingzone 29 can comprise one or more cooling stages operable to cool and atleast partially condense the predominantly methane stream in conduit109. In one embodiment, cooling zone 29 can be at least partly definedwithin one or more of the first or second refrigerant chillers 18, 21and/or within third refrigerant economizer 24. When a portion of coolingzone 29 is defined within one or more of first, second, and thirdrefrigeration cycles 13, 14, 15, in one embodiment, the respectiverefrigeration cycles can define one or more additional cooling passes.

In one embodiment depicted in FIG. 3, third refrigerant economizer 24can comprise one or more cooling stages operable to further cool thepressurized predominantly methane stream in conduit 104 via indirectheat exchange with the vaporizing refrigerant. In one embodiment, thetemperature of the pressurized LNG-bearing stream in conduit 105 can bereduced by an amount in the range of from about 2° C. (3.6° F.) to about35° C. (63° F.), about 3° C. (5.4° F.) to about 30° C. (54° F.), or 5°C. (9° F.) to 25° C. (45° F.) in third refrigerant economizer 24.Typically, the temperature of the pressurized LNG-bearing stream exitingthird refrigerant economizer 24 can be in the range of from about −170°C. (−274° F.) to about −55° C. (−67° F.), about −145° C. (−229° F.) toabout −70° C. (−94° F.), or −130° C. (−202° F.) to −85° C. (−121° F.).

As shown in FIG. 3, the cooled LNG-bearing stream exiting thirdrefrigerant economizer 24 can then be routed to expansion coolingsection 12, wherein the stream can be at least partially subcooled viasequential pressure reduction to near atmospheric pressure by passagethrough one or more expansion stages. Expansion cooling section 12 cancomprise in the range of from about 1 to about 6, about 2 to about 5, or3 to 4 expansion stages. In one embodiment, each expansion stage canreduce the temperature of the LNG-bearing stream by an amount in therange of from about 5° C. (9° F.) to about 35° C. (63° F.), about 7.5°C. (13.5° F.) to about 30° C. (54° F.), or 10° C. (18° F.) to 25° C.(45° F.). Each expansion stage comprises one or more expanders, whichreduce the pressure of the liquefied stream to thereby evaporate orflash a portion thereof. Examples of suitable expanders can include, butare not limited to, Joule-Thompson valves, venturi nozzles, andturboexpanders. In one embodiment of the present invention, expansionsection 12 can reduce the pressure of the LNG-bearing stream in conduit105 by an amount in the range of from about 520 kPa (75.4 psi) to about3,100 kPa (449.6 psi), about 860 kPa (124.7 psi) to about 2,070 kPa(300.2 psi), or 1,030 kPa (149.4 psi) to 1,550 kPa (224.8 psi).

Each expansion stage may additionally employ one or more vapor-liquidseparators operable to separate the vapor phase (i.e., the flash gasstream) from the cooled liquid stream. As previously discussed, thirdrefrigeration cycle 15 can comprise an open-loop refrigeration cycle,closed-loop refrigeration cycle, or any combination thereof. When thirdrefrigeration cycle 15 comprises a closed-loop refrigeration cycle, theflash gas stream exiting expansion section is generally employed as arefrigerant. When third refrigeration cycle 15 comprises an open-looprefrigeration cycle, at least a portion of the flash gas stream exitingexpansion section 12 be used as a refrigerant to cool at least a portionof the natural gas stream in conduit 104, and the remaining portion ofthe flash gas may be used in one or more locations internal or externalto the LNG facility. Generally, when third refrigerant cycle 15comprises an open-loop cycle, the third refrigerant can comprise atleast 50 weight percent, at least about 75 weight percent, or at least90 weight percent of flash gas from expansion section 12, based on thetotal weight of the stream. As illustrated in FIG. 3, the flash gasexiting expansion section 12 via conduit 106 can enter third refrigeranteconomizer 24, wherein the stream can cool at least a portion of thenatural gas stream entering third refrigerant economizer 24 via conduit104. The resulting warmed refrigerant stream can then exit thirdrefrigerant economizer 24 via conduit 108 and can thereafter be routedto an inlet port of third refrigerant compressor 22. As shown in FIG. 3,third refrigerant compressor 22 discharges a stream of compressed thirdrefrigerant, which is thereafter cooled in cooler 23. The resultingcooled methane stream in conduit 109 can then be further cooled incooling zone 29 before combining with the natural gas stream in conduit104 prior to entering third refrigerant economizer 24, as previouslydiscussed.

As shown in FIG. 3, the liquid stream exiting expansion section 12 viaconduit 107 can comprise LNG. In one embodiment, the LNG in conduit 107can have a temperature in the range of from about −130° C. (−202° F.) toabout −185° C. (−301° F.), about −145° C. (−229° F.) to about −170° C.(−274° F.), or −155° C. (−247° F.) to −165° C. (−265° F.) and a pressurein the range of from about 0 kPa (0 psia) to about 345 kPa (50 psia),about 35 kPa (5.1 psia) to about 210 kPa (30.5 psia), or 82.7 kPa (10.2psia) to 210 kPa (20.3 psia).

According to one embodiment, the LNG in conduit 107 can comprise atleast about 85 volume percent of methane, at least about 87.5 volumepercent methane, at least about 90 volume percent methane, at leastabout 92 volume percent methane, at least about 95 volume percentmethane, or at least 97 volume percent methane. In another embodiment,the LNG in conduit 107 can comprise less than about 15 volume percentethane, less than about 10 volume percent ethane, less than about 7volume percent ethane, or less than 5 volume percent ethane. In yetanother embodiment, the LNG in conduit 107 can have less than about 2volume percent C₃ ⁺ material, less than about 1.5 volume percent C₃ ⁺material, less than about 1 volume percent C₃ ⁺ material, or less than0.5 volume percent C₃ ⁺ material. In one embodiment (not shown), the LNGin conduit 107 can subsequently be routed to storage and/or shipped toanother location via pipeline, ocean-going vessel, truck, or any othersuitable transportation means. In one embodiment, at least a portion ofthe LNG can be subsequently vaporized for pipeline transportation or foruse in applications requiring vapor-phase natural gas.

Turning now to FIGS. 4a-b and 5a-b , multiple embodiments of specificconfigurations of LNG facilities as described previously with respect toFIG. 3 are illustrated. To facilitate an understanding of FIGS. 4a-b and5a-b , the following numeric nomenclature was employed. Items numbered31 through 49 correspond to process vessels and equipment directlyassociated with first propane refrigeration cycle 30, and items numbered51 through 69 correspond to process vessels and equipment related tosecond ethylene refrigeration cycle 50. Items numbered 71 through 94correspond to process vessels and equipment associated with thirdmethane refrigeration cycle 70 and/or expansion section 80. Itemsnumbered 96 through 99 are process vessels and equipment associated withheavies removal zone 95. Items numbered 100 through 199 correspond toflow lines or conduits that contain predominantly methane streams. Itemsnumbered 200 through 299 correspond to flow lines or conduits whichcontain predominantly ethylene streams. Items numbered 300 through 399correspond to flow lines or conduits that contain predominantly propanestreams. Items numbered 600 through 699 correspond to flow lines orconduits as well as process vessels and equipment associated with aninterstage cooling system depicted in FIG. 4b , while items numbered 700through 799 correspond to flow lines or conduits as well as processvessels and equipment associated with an interstage cooling systemdepicted in FIG. 5 b.

Referring first to FIGS. 4a and 4b , a cascade-type LNG facility inaccordance with one embodiment of the present invention is illustrated.The portion of the LNG facility depicted in FIG. 4a generally comprisesa propane refrigeration cycle 30, an ethylene refrigeration cycle 50, amethane refrigeration cycle 70 with an expansion section 80, and aheavies removal zone 95. While “propane,” “ethylene,” and “methane” areused to refer to respective first, second, and third refrigerants, itshould be understood that the embodiment illustrated in FIG. 4a anddescribed herein can apply to any combination of suitable refrigerants.The main components of propane refrigeration cycle 30 include a propanecompressor 31, a propane cooler 32, a high-stage propane chiller 33, anintermediate-stage propane chiller 34, and a low-stage propane chiller35. The main components of ethylene refrigeration cycle 50 include anethylene compressor 51, an ethylene cooler 52, a high-stage ethylenechiller 53, an optional first low-stage ethylene chiller 54, a secondlow-stage ethylene chiller/condenser 55, and an ethylene economizer 56.The main components of methane refrigeration cycle 70 include a methanecompressor 71, a methane cooler 72, a main methane economizer 73, and asecondary methane economizer 74. The main components of expansionsection 80 include a high-stage methane expander 81, a high-stagemethane flash drum 82, an intermediate-stage methane expander 83, anintermediate-stage methane flash drum 84, a low-stage methane expander85, and a low-stage methane flash drum 86.

The portion of the LNG facility depicted in FIG. 4a includes a heaviesremoval zone located downstream of optional first low-stage ethylenechiller 54 for removing heavy hydrocarbon components from the processednatural gas and recovering the resulting natural gas liquids. Theheavies removal zone 95 of FIG. 4a is shown as generally comprising afirst distillation column 96 and a second distillation column 97.

The LNG facility of FIGS. 4a and 4b also includes an interstage coolingsystem 600, depicted in FIG. 4b . Lines A-I illustrate how interstagesystem 600 is integrated in the LNG facility illustrated in FIG. 4a .Interstage cooling system 600 will be discussed in more detail shortlywith respect to FIG. 4 b.

The operation of the LNG facility illustrated in FIG. 4a will now bedescribed in more detail, beginning with propane refrigeration cycle 30.An inlet air (e.g., combustion air) stream in conduit A is introducedinto gas turbine driver 31 a, which is used to at least partially powerpropane compressor 31. Thereafter, a stream of partially compressed airis withdrawn from a low compression stage of gas turbine 31 a and routedto interstage cooling system 600 illustrated in FIG. 4b via conduit D,as shown in FIG. 4a . A stream of cooled, partially compressed airwithdrawn from interstage cooling system 600 in FIG. 4b can then beintroduced via conduit E into propane gas turbine 31 a, as illustratedin FIG. 4a . Additional details regarding the configuration andoperation of interstage cooling system 600 will be discussed in detailshortly.

In general, propane compressor 31 can be a multi-stage (e.g., threestage) compressor. In one embodiment, the three stages of compressionpreferably exist in a single unit, although each stage of compressionmay be a separate unit and the units may be mechanically coupled anddriven by a single driver. Upon compression, the propane is passedthrough conduit 300 to propane cooler 32, wherein it is cooled and atleast partially liquefied via indirect heat exchange with an externalfluid (e.g., air or water). A representative temperature and pressure ofthe liquefied propane refrigerant exiting cooler 32 is about 38° C.(100° F.) and about 1,310 kPa (190 psia).

As shown in FIG. 4a , the stream from propane cooler 32 can then enterconduit 302 and can be passed to a pressure reduction means, illustratedas expansion valve 36, wherein the pressure of the liquefied propane isreduced, thereby evaporating or flashing a portion thereof. Theresulting two-phase stream then flows via conduit 304 into high-stagepropane chiller 33. High stage propane chiller 33 uses indirect heatexchange means 37, 38, and 39 to cool respectively, the incoming gasstreams, including a yet-to-be-discussed methane refrigerant stream inconduit 112, a natural gas feed stream in conduit 110, and ayet-to-be-discussed ethylene refrigerant stream in conduit 202 viaindirect heat exchange with the vaporizing refrigerant. The cooledmethane refrigerant stream exits high-stage propane chiller 33 viaconduit 130 and can subsequently be routed to the inlet of main methaneeconomizer 73, which will be discussed in greater detail in a subsequentsection.

The cooled natural gas stream from high-stage propane chiller 33 (alsoreferred to herein as the “methane-rich stream”) flows via conduit 114to a separation vessel 40, wherein the gaseous and liquid phases areseparated. The liquid phase, which can be rich in propane and heaviercomponents (C₃+), is removed via conduit 303. The predominately vaporphase exits separator 40 via conduit 116 and can then enterintermediate-stage propane chiller 34, wherein the stream is cooled inindirect heat exchange means 41 via indirect heat exchange with ayet-to-be-discussed propane refrigerant stream. The resulting two-phasemethane-rich stream in conduit 118 can then be routed to low-stagepropane chiller 35, wherein the stream can be further cooled viaindirect heat exchange means 42. The resultant predominantly methanestream can then exit low-stage propane chiller 34 via conduit 120.Subsequently, the cooled methane-rich stream in conduit 120 can berouted to high-stage ethylene chiller 53, which will be discussed inmore detail shortly.

The vaporized propane refrigerant can be withdrawn from high-stagepropane chiller 33 via conduit 306 and can then be introduced into thehigh-stage suction port of propane compressor 31. The residual liquidpropane refrigerant in high-stage propane chiller 33 can be passed viaconduit 308 through a pressure reduction means, illustrated here asexpansion valve 43, whereupon a portion of the liquefied refrigerant isflashed or vaporized. The resulting cooled, two-phase refrigerant streamcan then enter intermediate-stage propane chiller 34 via conduit 310,thereby providing coolant for the natural gas stream andyet-to-be-discussed ethylene refrigerant stream enteringintermediate-stage propane chiller 34. The vaporized propane refrigerantexits intermediate-stage propane chiller 34 via conduit 312 and can thenenter the intermediate-stage inlet port of propane compressor 31. Theremaining liquefied propane refrigerant exits intermediate-stage propanechiller 34 via conduit 314 and is passed through a pressure-reductionmeans, illustrated here as expansion valve 44, whereupon the pressure ofthe stream is reduced to thereby flash or vaporize a portion thereof.The resulting vapor-liquid refrigerant stream then enters low-stagepropane chiller 35 via conduit 316 and cools the methane-rich andyet-to-be-discussed ethylene refrigerant streams entering low-stagepropane chiller 35 via conduits 118 and 206, respectively. The vaporizedpropane refrigerant stream then exits low-stage propane chiller 35 andis routed to the low-stage inlet port of propane compressor 31 viaconduit 318 wherein it is compressed and recycled as previouslydescribed.

As shown in FIG. 4a , a stream of ethylene refrigerant in conduit 202enters high-stage propane chiller, wherein the ethylene stream is cooledvia indirect heat exchange means 39. The resulting cooled stream inconduit 204 then exits high-stage propane chiller 33, whereafter thestream enters intermediate-stage propane chiller 34. Upon enteringintermediate-stage propane chiller 34, the ethylene refrigerant streamcan be further cooled via indirect heat exchange means 45. The resultingcooled ethylene stream can then exit intermediate-stage propane chiller34 prior to entering low-stage propane chiller 35 via conduit 206. Inlow-stage propane chiller 35, the ethylene refrigerant stream can be atleast partially condensed, or condensed in its entirety, via indirectheat exchange means 46. The resulting stream exits low-stage propanechiller 35 via conduit 208 and can subsequently be routed to aaccumulator 47, as shown in FIG. 4a . The liquefied ethylene refrigerantstream exiting accumulator 47 via conduit 212 can have a representativetemperature and pressure of about −30° C. (−22° F.) and about 2,032 kPa(295 psia).

Turning now to ethylene refrigeration cycle 50 in FIG. 4a , theliquefied ethylene refrigerant stream in conduit 212 can enter ethyleneeconomizer 56, wherein the stream can be further cooled by an indirectheat exchange means 57. The sub-cooled liquid ethylene stream in conduit214 can then be routed through a pressure reduction means, illustratedhere as expansion valve 58, whereupon the pressure of the stream isreduced to thereby flash or vaporize a portion thereof. The cooled,two-phase stream in conduit 215 can then enter high-stage ethylenechiller 53, wherein at least a portion of the ethylene refrigerantstream can vaporize to thereby cool the methane-rich stream entering anindirect heat exchange means 59 of high-stage ethylene chiller 53 viaconduit 120. The vaporized and remaining liquefied refrigerant exithigh-stage ethylene chiller 53 via respective conduits 216 and 220. Thevaporized ethylene refrigerant in conduit 216 can re-enter ethyleneeconomizer 56, wherein the stream can be warmed via an indirect heatexchange means 60 prior to entering the high-stage inlet port ofethylene compressor 51 via conduit 218, as shown in FIG. 4 a.

The remaining liquefied refrigerant in conduit 220 can re-enter ethyleneeconomizer 56, wherein the stream can be further sub-cooled by anindirect heat exchange means 61. The resulting cooled refrigerant streamexits ethylene economizer 56 via conduit 222 and can subsequently berouted to a pressure reduction means, illustrated here as expansionvalve 62, whereupon the pressure of the stream is reduced to therebyvaporize or flash a portion thereof. The resulting, cooled two-phasestream in conduit 224 enters optional first low-stage ethylene chiller54, wherein the refrigerant stream can cool the natural gas stream inconduit 122 entering optional first low-stage ethylene chiller 54 via anindirect heat exchange means 63. As shown in FIG. 4a , the resultingcooled methane-rich stream exiting intermediate stage ethylene chiller54 can then be routed to heavies removal zone 95 via conduit 124.Heavies removal zone 95 will be discussed in detail in a subsequentsection.

The vaporized ethylene refrigerant exits optional first low-stageethylene chiller 54 via conduit 226, whereafter the stream can combinewith a yet-to-be-discussed ethylene vapor stream in conduit 238. Thecombined stream in conduit 240 can enter ethylene economizer 56, whereinthe stream is warmed in an indirect heat exchange means 64 prior tobeing fed into the low-stage inlet port of ethylene compressor 51 viaconduit 230.

As shown in FIG. 4a , an inlet air (e.g., combustion air) stream inconduit B can be introduced into an ethylene compressor gas turbinedriver 51 a, which is used to at least partially power ethylenecompressor 51. Similarly to propane gas turbine 31 a, a stream ofpartially compressed air withdrawn from a lower stage of gas turbine 51a can be routed to interstage cooling system 600 depicted in FIG. 4b viaconduit F before being returned to a higher compression stage of gasturbine 51 a via conduit G, as shown in FIG. 4a . In general, ethylenecompressor 51 can comprise one or more compression stages. In oneembodiment, three stages of compression preferably exist in a singleunit, although each stage of compression may be a separate unit and theunits may be mechanically coupled and driven by a single driver. Uponcompression, a stream of compressed ethylene refrigerant in conduit 236can subsequently be routed to ethylene cooler 52, wherein the ethylenestream can be cooled via indirect heat exchange with an external fluid(e.g., water or air). The resulting, at least partially condensedethylene stream can then be introduced via conduit 202 into high-stagepropane chiller 33 for additional cooling as previously described.

The remaining liquefied ethylene refrigerant exits optional firstlow-stage ethylene chiller 54 via conduit 228 prior to entering secondlow-stage ethylene chiller/condenser 55, wherein the refrigerant cancool the methane-rich stream exiting heavies removal zone 95 via conduit126 via indirect heat exchange means 65 in second low-stage ethylenechiller/condenser 55. As shown in FIG. 4a , the vaporized ethylenerefrigerant can then exit second low-stage ethylene chiller/condenser 55via conduit 238 prior to combining with the vaporized ethylene exitingoptional first low-stage ethylene chiller 54 and entering the low-stageinlet port of ethylene compressor 51, as previously discussed.

The cooled natural gas stream exiting low-stage ethylenechiller/condenser can also be referred to as the “pressurizedLNG-bearing stream.” As shown in FIG. 4a , the pressurized LNG-bearingstream exits second low-stage ethylene chiller/condenser 55 via conduit132 prior to entering main methane economizer 73. In main methaneeconomizer 73, the methane-rich stream can be cooled in an indirect heatexchange means 75 via indirect heat exchange with one or more yet-to-bediscussed methane refrigerant streams. The cooled, pressurizedLNG-bearing stream exits main methane economizer 73 and can then berouted via conduit 134 into expansion section 80 of methanerefrigeration cycle 70. In expansion section 80, the cooledpredominantly methane stream passes through high-stage methane expander81, whereupon the pressure of the stream is reduced to thereby vaporizeor flash a portion thereof. The resulting two-phase methane-rich streamin conduit 136 can then enter high-stage methane flash drum 82,whereupon the vapor and liquid portions can be separated. The vaporportion exiting high-stage methane flash drum 82 (i.e., the high-stageflash gas) via conduit 143 can then enter main methane economizer 73,wherein the stream is heated via indirect heat exchange means 76. Theresulting warmed vapor stream exits main methane economizer 73 viaconduit 138 and subsequently combines with a yet-to-be-discussed vaporstream exiting heavies removal zone 95 in conduit 140. The combinedstream in conduit 141 can then be routed to the high-stage inlet port ofmethane compressor 71, as shown in FIG. 4 a.

The liquid phase exiting high-stage methane flash drum 82 via conduit142 can enter secondary methane economizer 74, wherein the methanestream can be cooled via indirect heat exchange means 92. The resultingcooled stream in conduit 144 can then be routed to a second expansionstage, illustrated here as intermediate-stage expander 83.Intermediate-stage expander 83 reduces the pressure of the methanestream passing therethrough to thereby reduce the stream's temperatureby vaporizing or flashing a portion thereof. The resulting two-phasemethane-rich stream in conduit 146 can then enter intermediate-stagemethane flash drum 84, wherein the liquid and vapor portions of thestream can be separated and can exit the intermediate-stage flash drumvia respective conduits 148 and 150. The vapor portion (i.e., theintermediate-stage flash gas) in conduit 150 can re-enter secondarymethane economizer 74, wherein the stream can be heated via an indirectheat exchange means 87. The warmed stream can then be routed via conduit152 to main methane economizer 73, wherein the stream can be furtherwarmed via an indirect heat exchange means 77 prior to entering theintermediate-stage inlet port of methane compressor 71 via conduit 154.

The liquid stream exiting intermediate-stage methane flash drum 84 viaconduit 148 can then pass through a low-stage expander 85, whereupon thepressure of the liquefied methane-rich stream can be further reduced tothereby vaporize or flash a portion thereof. The resulting cooled,two-phase stream in conduit 156 can then enter low-stage methane flashdrum 86, wherein the vapor and liquid phases can be separated. Theliquid stream exiting low-stage methane flash drum 86 can comprise theliquefied natural gas (LNG) product. The LNG product, which is at aboutatmospheric pressure, can be routed via conduit 158 downstream forsubsequent storage, transportation, and/or use.

The vapor stream exiting low-stage methane flash drum (i.e., thelow-stage methane flash gas) in conduit 160 can be routed to secondarymethane economizer 74, wherein the stream can be warmed via an indirectheat exchange means 89. The resulting stream can exit secondary methaneeconomizer 74 via conduit 162, whereafter the stream can be routed tomain methane economizer 73 to be further heated via indirect heatexchange means 78. The warmed methane vapor stream can then exit mainmethane economizer 73 via conduit 164 prior to being routed to thelow-stage inlet port of methane compressor 71.

Methane compressor 71 can comprise one or more compression stages and,can be at least partially driven by a gas turbine driver 71 a. Similarlyto propane gas turbine 31 a and ethylene gas turbine 51 a, a stream ofpartially compressed air withdrawn from a lower stage of methane gasturbine 71 a can be routed to interstage cooling system 600 depicted inFIG. 4b via conduit H before being returned to methane gas turbine 71 avia conduit I, as shown in FIG. 4a . In one embodiment, methanecompressor 71 comprises three compression stages in a single module. Inanother embodiment, the compression modules can be separate, but can bemechanically coupled to gas turbine driver 71 a. As shown in FIG. 4a ,the compressed methane refrigerant stream exiting methane compressor 71can be discharged into conduit 166, whereafter the stream can be cooledvia indirect heat exchange with an external fluid (e.g., air or water)in methane cooler 72. The cooled methane refrigerant stream exitingmethane cooler 72 can then enter conduit 112, whereafter the methanerefrigerant stream can be further cooled in propane refrigeration cycle30, as described in detail previously.

Upon being cooled in propane refrigeration cycle 30, the methanerefrigerant stream can be discharged into conduit 130 and subsequentlyrouted to main methane economizer 73, wherein the stream can be furthercooled via indirect heat exchange means 79. The resulting sub-cooledstream exits main methane economizer 73 via conduit 168 and can thencombined with the heavies-depleted stream exiting heavies removal zone95 via conduit 126, as previously discussed.

Turning now to heavies removal zone 95, at least a portion of thepredominantly methane stream withdrawn from optional first low-stageethylene chiller 54 via conduit 124 can subsequently be introduced intofirst distillation column 96. As shown in FIG. 2, at least a portion ofa predominantly vapor overhead stream withdrawn from first distillationcolumn 96 can subsequently be routed to second low-stage ethylenechiller condenser 55, wherein the stream can be further cooled viaindirect heat exchange means 65, as discussed in detail previously. Apredominantly liquid, heavies-rich bottoms stream withdrawn from firstdistillation column 96 via conduit 170 can then be introduced intosecond distillation column 97. The predominantly liquid bottoms streamexiting second distillation column 97 via conduit 171, which generallycomprises NGL, can be routed out of heavies removal zone 95 forsubsequent storage, processing, and/or future use. The predominantlyvapor overhead stream withdrawn from second distillation column 97 canbe routed via conduit 140 to one or more locations within the LNGfacility. In one embodiment, the stream can be introduced into thehigh-stage suction port of methane compressor 71. In another embodiment,the stream can be routed to storage or subjected to further processingand/or use.

Turning now to FIG. 4b , one embodiment of an interstage cooling system600 is illustrated as generally comprising a primary heat exchanger 602and a secondary heat exchanger 604. Turning to the operation of theinterstage cooling system 600 illustrated in FIG. 4b , a stream ofuncompressed combustion air can be introduced into primary heatexchanger 602, wherein the stream can be cooled in an indirect heatexchange means 608 via indirect heat exchange with a cooled stream ofprimary coolant entering heat exchanger 602 via conduit 654. Theresulting cooled air stream in conduit 650 can be routed to gas turbines31 a, 51 a, 71 a of respective propane, ethylene, and methane 31, 51, 71compressors via respective conduits A, B, C, as illustrated in FIG. 4 a.

As discussed briefly with respect to FIG. 4a , partially compressed airstreams withdrawn from low compression stages of respective gas turbines31 a, 51 a, and 71 a can be routed to warm fluid inlets of primary heatexchanger 602, as shown in FIG. 4b . In primary heat exchanger 602, thepartially compressed air streams in conduits D, F, H can be cooled viarespective indirect heat exchange means 606 a-c to thereby providecooled, partially compressed air streams in conduits E, G, I. As shownin FIG. 4b , at least a portion of these cooled, compressed air streamscan subsequently be routed to a higher compression stage of gas turbines31 a, 51 a, and 71 a, as discussed previously with respect to FIG. 4 a.

Referring back to FIG. 4b , the primary coolant stream in conduit 656can be introduced into secondary heat exchanger 604, wherein the streamcan be cooled in indirect heat exchange means 612 via indirect heatexchange with a stream of secondary coolant entering secondary heatexchanger 604 via conduit 658. The resulting warmed stream of secondarycoolant can be routed to another location for subsequent processing,storage, use, and/or disposal, while the stream of cooled primarycoolant can be reintroduced into primary heat exchanger 602 via conduit654 to cool one or more air streams as discussed previously.

Turning now to FIGS. 5a and 5b , an LNG facility configured inaccordance with another embodiment of the present invention isillustrated. The LNG facility configuration illustrated in FIGS. 5a and5b is similar to the LNG configuration previously described with respectto FIGS. 4a and 4b , above, with like numerals designating likecomponents. The operation of the LNG facility depicted in FIG. 5a , asit differs from the operation of the embodiment previously describedwith respect to FIG. 4a , will now be described in detail.

As shown in FIG. 5a , inlet air streams in conduits A, B, C can beintroduced into combustion air inlets of respective gas turbines 31 a,51 a, and 71 a used to at least partially drive propane, ethylene, andmethane compressors 31, 51, 71. Subsequently, streams of partiallycompressed air withdrawn from lower stages of gas turbines 31 a, 51 a,71 a can be routed to interstage cooling system 700 depicted in FIG. 5bvia respective conduits E, H, K before being returned to gas turbines 31a, 51 a, 71 a via respective conduits G, J, M as shown in FIG. 5a .Interstage cooling system 700, illustrated in FIG. 5b , will bediscussed in detail shortly.

As illustrated in FIG. 5a , a stream of compressed propane dischargedfrom propane compressor 31 in conduit 300 can subsequently be passedthrough propane cooler 32. The resulting cooled, at least partiallyliquefied stream can then pass through pressure reduction mean 36 and,thereafter, the stream in conduit 302 can be split into two portions.The first portion, in conduit 304, can be introduced into high-stagepropane chiller 33 and can be used to cool the natural gas streamentering the LNG facility via conduit 110, as discussed previously. Thesecond portion of the refrigerant stream in conduit 302 can be routedvia conduit D to interstage cooling system 700, illustrated in FIG. 5b .Subsequently, warmed refrigerant streams in conduits F, I, L frominterstage cooling system 700 in FIG. 5b can respectively be returned tohigh-stage, intermediate-stage, and low-stage suction ports of propanecompressor 31, as shown in FIG. 5 a.

Turning now to FIG. 5b , another embodiment of an interstage coolingsystem 700 is illustrated as generally comprising first, second, andthird interstage coolers 702, 704, 706. In operation, a combustion airstream in conduit 750 a and a stream of partially compressed airwithdrawn from a low compression stage of propane gas turbine 31 a inconduit E can be introduced into first interstage cooler 702. As shownin FIG. 5b , a stream of cooled propane refrigerant withdrawn from thedischarge of propane compressor 31 in FIG. 5a can be introduced intofirst interstage cooler 702 via conduit D, as shown in FIG. 5b . Infirst interstage cooler 702, the combustion air stream and partiallycompressed air stream can be cooled via indirect heat exchange with thevaporizing refrigerant via respective indirect heat exchange means 706 aand 706 b. The resulting cooled combustion air stream and the cooled,partially compressed air stream can be withdrawn from first interstagecooler 702 via respective conduits A and G.

Thereafter, the cooled air streams can be respectively routed to acombustion air inlet and one or more compression stages of gas turbine31 a, as illustrated in and discussed previously with respect to FIG. 5a. As shown in FIG. 5b , a stream of warmed, vaporized propanerefrigerant can be withdrawn from a warm refrigerant outlet of firstinterstage cooler 702 and can subsequently be routed to the high-stagesuction port of propane compressor via conduit F, as shown in FIG. 5a ,while the remaining, predominantly liquid propane refrigerant can exitfirst interstage cooler 702 via conduit 752, as illustrated in FIG. 5 b.

Prior to entering second interstage cooler 704, the stream ofpredominantly liquid propane refrigerant can pass through an optionalpressure reduction means, illustrated here as expansion valve 710,wherein the pressure of the stream can be reduced, evaporating orflashing a portion thereof. The resulting refrigerant stream can then beintroduced into a cool refrigerant inlet of second interstage cooler704. In second interstage cooler 704, a stream of uncompressedcombustion air in conduit 750 b and a stream of partially compressed airwithdrawn from a low compression stage of ethylene gas turbine 51 a inconduit H can be cooled via indirect heat exchange with the vaporizingpropane refrigerant in respective indirect heat exchange means 708 a and708 b. A stream of vaporized propane refrigerant can be withdrawn fromsecond interstage cooler 704 via conduit I and can then be introducedinto the intermediate-stage suction port of propane compressor 31, asshown in FIG. 5a . The resulting cooled combustion air stream withdrawnfrom second interstage cooler 704 via conduit B, as shown in FIG. 5b ,can subsequently be routed to a combustion air inlet of gas turbine 51a, while the cooled partially compressed air stream withdrawn fromsecond interstage cooler 704 via conduit J can be introduced into ahigher compression stage of gas turbine 51 a, as illustrated in FIG. 5a.

According to one embodiment depicted in FIG. 5b , the remainingpredominantly liquid propane stream withdrawn from second interstagecooler 704 via conduit 754 can optionally pass through a pressurereduction means, illustrated here as expander 712. The resultingrefrigerant stream can then be introduced into a warm refrigerant inletof third interstage cooler 706, wherein the stream can at leastpartially cool the stream of uncompressed combustion air in conduit 750c and the stream of partially compressed air withdrawn from a lowcompression stage of methane gas turbine 71 a, illustrated in FIG. 5a ,in conduit K via respective indirect heat exchange means 714 a and 714b, as shown in FIG. 5b . The resulting, predominantly vaporized propanerefrigerant stream withdrawn from third interstage cooler 706 viaconduit L can subsequently be routed to the low-stage suction port ofpropane compressor 31, as illustrated in FIG. 5 a.

In one embodiment of the present invention, the LNG production systemsillustrated in FIGS. 1-3, 4 a, 4 b, 5 a, and 5 b can be simulated on acomputer using conventional process simulation software in order togenerate process simulation data in a human-readable form. In oneembodiment, the process simulation data can be in the form of a computerprint out. In another embodiment, the process simulation data can bedisplayed on a screen, a monitor, or other viewing device. Thesimulation data can then be used to manipulate the LNG system. In oneembodiment, the simulation results can be used to design a new LNGfacility and/or revamp or expand an existing facility. In anotherembodiment, the simulation results can be used to optimize the LNGfacility according to one or more operating parameters. Examples ofsuitable software for producing the simulation results include HYSYS™ orAspen Plus® from Aspen Technology, Inc., and PRO/I®(t from SimulationSciences Inc.

Numerical Ranges

The present description uses numerical ranges to quantify certainparameters relating to the invention. It should be understood that whennumerical ranges are provided, such ranges are to be construed asproviding literal support for claim limitations that only recite thelower value of the range as well as claims limitation that only recitethe upper value of the range. For example, a disclosed numerical rangeof 10 to 100 provides literal support for a claim reciting “greater than10” (with no upper bounds) and a claim reciting “less than 100” (with nolower bounds).

Definitions

As used herein, the terms “a,” “an,” “the,” and “said” mean one or more.

As used herein, the term “aeroderivative gas turbine” refers to a gasturbine having a design based on an aircraft engine that has beenadapted for industrial use.

As used herein, the term “and/or,” when used in a list of two or moreitems, means that any one of the listed items can be employed by itself,or any combination of two or more of the listed items can be employed.For example, if a composition is described as containing components A,B, and/or C, the composition can contain A alone; B alone; C alone; Aand B in combination; A and C in combination; B and C in combination; orA, B, and C in combination.

As used herein, the term “cascade-type refrigeration process” refers toa refrigeration process that employs a plurality of refrigerationcycles, each employing a different pure component refrigerant tosuccessively cool natural gas.

As used herein, the term “closed-loop refrigeration cycle” refers to arefrigeration cycle wherein substantially no refrigerant enters or exitsthe cycle during normal operation.

As used herein, the terms “comprising,” “comprises,” and “comprise” areopen-ended transition terms used to transition from a subject recitedbefore the term to one or elements recited after the term, where theelement or elements listed after the transition term are not necessarilythe only elements that make up of the subject.

As used herein, the terms “containing,” “contains,” and “contain” havethe same open-ended meaning as “comprising,” “comprises,” and“comprise,” provided above.

As used herein, the terms “economizer” or “economizing heat exchanger”refer to a configuration utilizing a plurality of heat exchangersemploying indirect heat exchange means to efficiently transfer heatbetween process streams.

As used herein, the term “fluid flow communication” between twocomponents means that at least a portion of the fluid or material fromthe first component enters, passes through, or otherwise comes intocontact with the second component.

As used herein, the terms “having,” “has,” and “have” have the sameopen-ended meaning as “comprising,” “comprises,” and “comprise,”provided above.

As used herein, the terms “heavy hydrocarbon” and “heavies” refer to anycomponent that is less volatile (i.e., has a higher boiling point) thanmethane.

As used herein, the terms “including,” “includes,” and “include” havethe same open-ended meaning as “comprising,” “comprises,” and“comprise,” provided above.

As used herein, the term “mid-range standard boiling point” refers tothe temperature at which half of the weight of a mixture of physicalcomponents has been vaporized (i.e., boiled off) at standard pressure.

As used herein, the term “mixed refrigerant” refers to a refrigerantcontaining a plurality of different components, where no singlecomponent makes up more than 65 mole percent of the refrigerant.

As used herein, the term “modular” refers to a turbine havinginterchangeable segments.

As used herein, the term “natural gas” means a stream containing atleast about 60 mole percent methane, with the balance being inerts,ethane, higher hydrocarbons, nitrogen, carbon dioxide, and/or a minoramount of other contaminants such as mercury, hydrogen sulfide, andmercaptan.

As used herein, the terms “natural gas liquids” or “NGL” refer tomixtures of hydrocarbons whose components are, for example, typicallyheavier than methane. Some examples of hydrocarbon components of NGLstreams include ethane, propane, butane, and pentane isomers, benzene,toluene, and other aromatic compounds.

As used herein, the term “open-loop refrigeration cycle” refers to arefrigeration cycle wherein at least a portion of the refrigerantemployed during normal operation originates from the fluid being cooledby the refrigerant cycle.

As used herein, the terms “predominantly,” “primarily,” “principally,”and “in major portion,” when used to describe the presence of aparticular component of a fluid stream, means that the fluid streamcomprises at least 50 mole percent of the stated component. For example,a “predominantly” methane stream, a “primarily” methane stream, a stream“principally” comprised of methane, or a stream comprised “in majorportion” of methane each denote a stream comprising at least 50 molepercent methane.

As used herein, the term “pure component refrigerant” means arefrigerant that is not a mixed refrigerant.

As used herein, the terms “upstream” and “downstream” refer to therelative positions of various components of a natural gas liquefactionfacility along a fluid flow path in an LNG facility. For example, acomponent A is located downstream of another component B if component Ais positioned along a fluid flow path that has already passed throughcomponent B. Likewise, component A is located upstream of component B ifcomponent A is located on a fluid flow path that has not yet passedthrough component B.

CLAIMS NOT LIMITED TO DISCLOSED EMBODIMENTS

The preferred forms of the invention described above are to be used asillustration only, and should not be used in a limiting sense tointerpret the scope of the present invention. Modifications to theexemplary embodiments, set forth above, could be readily made by thoseskilled in the art without departing from the spirit of the presentinvention.

The inventors hereby state their intent to rely on the Doctrine ofEquivalents to determine and assess the reasonably fair scope of thepresent invention as pertains to any apparatus not materially departingfrom but outside the literal scope of the invention as set forth in thefollowing claims.

What is claimed is:
 1. A process for liquefying a natural gas stream,the process comprising: (a) cooling at least a portion of the naturalgas stream via indirect heat exchange with a first refrigerant in afirst refrigeration cycle to produce a cooled natural gas stream; (b)further cooling at least a portion of the cooled natural gas stream viaindirect heat exchange with a second refrigerant in a secondrefrigeration cycle to provide a further cooled natural gas stream; and(c) partially compressing an air stream with a low compression stage toprovide a partially compressed air stream; (d) cooling the air streamand the partially compressed air stream via indirect heat exchanger witha primary coolant selected from the group consisting of: the firstrefrigerant, the second refrigerant, and any combination thereof, toprovide a cooled inlet air stream and a cooled partially compressed airstream, wherein the partially compressed air stream is withdrawn from anintermediate compression stage of a gas turbine used to drive at leastone refrigerant compressor associated with the first or the secondrefrigeration cycle, or both; and (e) introducing the cooled inlet airstream into an inlet of the gas turbine.
 2. The process of claim 1,wherein the cooling step (d) results in a warmed primary coolant stream;further comprising cooling at least a portion of the warmed primarycoolant stream via indirect heat exchange with a secondary coolantstream to thereby provide a cooled primary coolant stream and using atleast a portion of the cooled primary coolant stream to accomplish atleast a portion of the cooling step (d).
 3. The process of claim 2,wherein the secondary coolant stream comprises air.
 4. The process ofclaim 1, wherein the first and second refrigerants are each comprisedpredominately of hydrocarbons.
 5. The process of claim 1, wherein thefirst refrigerant is comprised predominately of propane, propylene,ethane, or ethylene.
 6. The process of claim 1, wherein the firstrefrigerant is comprised predominately of propane.
 7. The process ofclaim 6, wherein the second refrigerant is a mixed hydrocarbonrefrigerant.
 8. The process of claim 6, wherein the second refrigerantis comprised predominately of ethane, ethylene, methane, or nitrogen. 9.The process of claim 1, wherein the cooling of step (d) cools thepartially compressed air stream to a temperature that is at least 1° C.cooler than the temperature of an uncompressed air stream being suppliedto the inlet of the gas turbine.
 10. The process of claim 1, wherein thepartially compressed air steam and the air stream are cooled in a commonheat exchanger.
 11. The process of claim 1, wherein the gas turbine isdual-shaft or triple-shaft gas turbine.
 12. The process of claim 11,wherein the gas turbine is a triple-shaft gas turbine.
 13. The processof claim 12, wherein the first refrigerant is predominately comprised ofpropane, wherein the second refrigerant is a mixed hydrocarbonrefrigerant.
 14. The process of claim 13, further comprising cooling atleast a portion of the further cooled natural gas stream in a thirdrefrigeration cycle, wherein the third refrigeration cycle comprises anitrogen refrigeration cycle.
 15. The process of claim 1, furthercomprising cooling at least a portion of the further cooled natural gasstream in a third refrigeration cycle, wherein the third refrigerationcycle comprises and open-loop methane refrigeration cycle.
 16. Theprocess of claim 1, further comprising, intermediate to step (b),separating at least a portion of the cooled natural gas stream in aheavies removal column to provide a predominately methane overheadproduct and a heavies-rich bottom product, wherein the further coolednatural gas stream comprises at least a portion of the predominatelymethane overhead product.
 17. The process of claim 1, wherein the firstand the second refrigerants are pure-component refrigerants, wherein thefirst and second refrigerants have different compositions.
 18. Theprocess of claim 1, further comprising introducing the cooled partiallycompressed air stream to a high compression stage of the gas turbine.19. A process for liquefying a natural gas stream, the processcomprising: (a) compressing a first refrigerant stream in a firstrefrigerant compressor to provide a first compressed refrigerant stream,wherein the first refrigerant compressor is at least partially driven bya first gas turbine; (b) compressing a first air stream with a lowcompression stage to provide a partially compressed air stream; (c)cooling the partially compressed air stream via indirect heat exchangewith at least a portion of the first compressed refrigerant stream toprovide a first cooled air stream and a cooled partially compressed airstream; and (d) introducing at least a portion of the first cooled airstream into the first gas turbine.
 20. The process of claim 19, furthercomprising cooling a second air stream via indirect heat exchange withthe first refrigerant to provide a second cooled air stream andintroducing the second cooled air stream into first gas turbine, whereinthe second air stream is an uncompressed air stream, wherein the secondcooled air stream is introduced into the low compression stage of thefirst gas turbine.
 21. The process of claim 19, further comprisingcooling a second air stream via indirect heat exchange with the firstrefrigerant to provide a second cooled air stream and introducing thesecond cooled air stream into a second gas turbine used to power asecond refrigerant compressor operable to compress a second refrigerantsystem.
 22. The process of claim 21, wherein the first and the secondrefrigerant streams have different compositions.
 23. The process ofclaim 22, wherein the first and the second refrigerant streams arecomprised predominately of hydrocarbons.
 24. The process of claim 21,wherein the first refrigerant stream comprises predominately propane,wherein the second refrigerant stream comprises predominately ethylene,ethane, nitrogen, or methane.
 25. The process of claim 24, furthercomprising using at least a portion of the first and the secondrefrigerant streams to cool the natural gas stream to provide a coolednatural gas stream and further cooling the cooled natural gas stream viaindirect heat exchange with a third predominately methane refrigerant.26. The process of claim 21, wherein the first refrigerant is comprisedpredominately of propane, wherein the second refrigerant is a mixedhydrocarbon refrigerant.
 27. The process of claim 19, wherein thecooling step (b) cools the first air stream by no more than 25° C.,wherein none of the cooling of step (b) is accomplished via direct heatexchange.
 28. The process of claim 19, wherein the first gas turbine isa multi-shaft gas turbine.
 29. The process of claim 19, furthercomprising introducing the cooled partially compressed air stream to ahigh compression stage of the gas turbine.
 30. A liquefied natural gas(LNG) facility, the LNH facility comprising: a first refrigeration cyclecomprising a first refrigerant compressor, a first refrigerant chiller,and a first gas turbine, wherein the first refrigerant compressor isoperable to produce a compressed first refrigerant stream and the firstrefrigerant chiller is operable to cool a natural gas stream viaindirect heat exchange with the compressed first refrigerant stream toproduce a cooled natural gas stream, wherein the first compressor isdriven by the first gas turbine, wherein the first gas turbine is amulti-shaft gas turbine comprising a first low compression stage and afirst high compression stage; and a first heat exchange zone operable tocool a first partially compressed air stream withdrawn from the firstlow compression stage via indirect heat exchange with the compressedfirst refrigerant stream to produce a first cooled air stream, whereinthe first high compression stage is configured to receive the firstcooled air stream.
 31. The facility of claim 30, further comprising asecond refrigeration cycle comprising a second refrigerant compressoroperable to produce a compressed second refrigerant stream and a secondrefrigerant chiller operable to cool the cooled natural gas stream viaindirect heat exchange with the compressed second refrigerant stream,wherein the second compressor is driven by a second multi-stage,multi-shaft gas turbine, wherein the second gas turbine comprises asecond low compression stage and a second high compression stage, thefirst heat exchange zone further operable to cool a second partiallycompressed air stream withdrawn from the second low compression stagevia indirect heat exchange with said first coolant to produce a secondcooled air stream, wherein the second high compression stages isoperable to receive the second cooled air stream.
 32. The facility ofclaim 30, wherein the first refrigeration cycle comprises a closed-looppropane refrigeration cycle, wherein the second refrigeration cyclecomprises a mixed refrigerant cycle.
 33. The facility of claim 30,wherein the first refrigeration cycle comprises a closed-loop propanerefrigeration cycle, wherein the second refrigeration cycle comprises aclosed loop refrigeration cycle, wherein the second refrigerationcomprises predominately ethane, ethylene, or nitrogen.
 34. The facilityof claim 30, wherein the first heat exchange zone comprises a singleheat exchanger.
 35. The facility of claim 30, wherein the multi-stage,multi-shaft first gas turbine is a triple-shaft gas turbine.